1. Field of the Invention
This invention relates to an optical grating assembly wherein the grating pitch is variable.
2. Summary of the Prior Art
It has been previously proposed to provide an optical grating and a piezo-electric element in a device forming a modulator and comprising a piezo-electric crystal on one mirror face of which is engraved a grating. The crystal is excited by means of two electrodes applied to two other faces of the grating, these two other faces facing each other and being perpendicular to the engraced face. This device is arranged to vary the pitch of the grating about a mean value, the modulation of the spacing between the lines of the grating causing a corresponding modulation of a light beam diffracted by the grating. In order to excite the crystal, it is necessary to apply a very high voltage of the order of 10,000 volts.
This previously proposed modulator is disadvantageous owing to the very high voltages required to operate it and its limited range of grating pitch variations.
It is an object of the present invention to provide an improved variable pitch optical grating. It is a further object to provide an optical grating assembly for use in industry at readily available voltages.